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HOG'S FAT                                        ^5

The digitonides thus obtained are boiled for 15-20 minutes, in a flask
fitted with a reflux condenser, with about 20 c.c. of acetic anhydride, the
liquid being then evaporated to dryness in a glass dish on the water-bath,
the mass being stirred towards the end with a glass rod. The residue is
recrystaUised several times from 95-96% alcohol and the melting-point of
the acetyl-compound thus obtained determined after the second, third or
fourth crystallisation.

Melting point oj the acetyl-compound. This is determined in a very
thin glass U-tabe, into one branch of which the powdered substance is
introduced to form a layer 2-3 mm. deep. The observed melting point
is then corrected by means of the formula,

x = T + [( T t) X 0-000154],

where x = correct melting point,

T = observed melting point,

n  length of meicury column of thermometer protruding from the
bath, expressed in degrees,1

t = mean temperature of the air about the protruding part of the
thermometer, determined with another thermometer placed near the first
and with its bulb at the middle of the protruding portion of the stem.2

The corrected melting point of cholesterol acetate is ii4'3-ii4-S, whilst
that of phytosterol acetate is above 125.

(d) Rotatory power. This is determined on the fat as such or on the
unsaponifiable substances extracted from it. In the former case, which
serves for the detection of Hydnocarpus oil, the rotatory power of the fat
is determined in benzene solution at a temperature of about 20 with an
ordinary shadow polarimeter. From the observed rotation the specific
rotation [ajf," is calculated by means of the formula,

r .,9n     iooa


where a is the observed angle in circular degrees, I the length in decimetres
of the tube used, and c the concentration, i.e., the number of grams of sub-
stance in 100 c.c. of the solution.

The determination of the rotatory power of the unsaponifiable substance
is effected in the manner indicated by Berg and Angerhausen for the detec-
tion of Mowrah butter in lard.3

* *

Genuine hog's fat should not contain appreciable quantities of water, alkaline
substances or other mineral matters, and should be free from all extraneous
fats and oils.

Its physical and chemical characters should lie within the limits given in
Table XLVII. A saponification number above 200, volatile acid and Polenske
numbers higher than i, and an iodine number below 45 demonstrate the presence

* For instance, if the thermometer is immersed up to + 5 and the observed melting
point is 115, n = 115  5.

2  For melting points between 100 and 150,*! = 50-56 .

3  Zeitschr. Unt. Nahr. Genussmittel, 1914, XXVII, p. 723.bine with the digitonin forming insoluble products (digitonidas), which